Stoker control system



Patented Feb. 3, 1942 UNITED. STATES PATENT OFFICE 2,271,831 .4 STOKER. CONTROL SYSTEM Ernest T. Selig, Jr., Kansas City, Mo.

Application September 23, 1940, Serial No. 357,964

11 Claims.

This invention relates to a control system for automatic stokers, and the main object of the invention is to devise a control system which will substantially reduce and/or eliminate the blowing of ash from the stoker. This application is, in part, a continuation of my copending application Ser. No. 163,870, filed September 14, 1937, now Patent No. 2,218,859 dated October 22, 1940.

In domestic heating systems using coal as a fuel and employing automatic means for intermittently supplying fuel to the burner, thev fuel burns down during the shut-down periods, leaving a ring of ash around the burner'or tuyere, and, upon starting up again, the blower supplying air to the burner blows the ash out of the burner, and this ash, passing through cracks in the combustion chamber and smoke pipe,.passes out into the room and becomes a source of considerable annoyance. The fine ash that is carried out of the furnace in the manner described is commonly known as fly-ash.

According to my invention, I substantially eliminate the difficulty of fly-ash by arranging theh control system so that upon starting up after each shut-down period, the full blast of air is not supplied immediately upon starting of the fuel-feed device, but means are provided to delay the application of the full blast of air for a time sufiicient to allow the fuel-feeding mechanism to feed enough coal to the burner to displace the ash from directly above the air nozzle or tuyere. In this manner, the fiy-ash is removed from the direct path of the air blast supplied to the burner, and it drops down into' the ashpit without being blown up into the combustion chamber.

A number of embodiments of'my invention are which:

Figure 1 is a diagrammatic view illustrating my invention applied to a coal-burnin -auto-' in which the air is controlled by a damper in the g blower outlet duct;

Figure 3 illustrates a, modified form of control in which the damper is operated by an electromagnet which turn is controlled by the timedelay device; and 1' damper 61) arranged over the inlet port of the illustrated in the accompanyin drawing, in,

Figure 4 illustrates a modified control system in which separate motors are employed for driving the blower and the fuel feed device.

Referring to Figure 1, a heating furnace of any suitable construction is indicated at I, the furnace being provided with an ash-pit la, acombustion chamber lb, and afiue to. A smoke pipe volves a rotary screw conveyor located in the duct 8a, although other types of conveyors may be used. c

The motor 1, which drives the fuel feed mechanism and the blower 6, is energized from a suitable electric supply circuit indicated. at 9, and the operation Of the motoris controlled by a thermostatic switch ID in accordance with the temperature or heat demands of the space in which the switch l0 islocated. Thermostat I0 is usually, but not necessarily, located in one of the'first floor rooms. The motor I is preferably also energized at periodic intervals independently of the condition of the thermostat [0 by means of known control mechanism indicated at H. This mechanism may assume various known forms. One suitable arrangement is shown in the patent to Gray et a1. 1,667,001. It should be understood that theautomaticcontrol ll need not be employed,'and the motor can be controlled directly vby the thermostatic switch to, if desired.

The blower -6 is provided with an, adjustable blower for controlling the amount of air supplied to the. burner. The damper 6b is arranged to be operated by a time-delay device (indicated at [2) which becomes effective a predetermined time after the motor 1 begins to operate. This time-delay device may assume various forms, andthree different constructions are shown in Figures 1a, 1b and 1c.

The time-delay device of Figure 1a is mounted in a suitable casing or frame l2a and consists of a worm gear l1 mounted on a shaft Ila which is driven from the motor I, which supplies fuel to'the furnace, preferably at a slow speed by means of a suitable speed-reducing gear, such as by a gear l2b driven by a worm on the motor shaft. The thread on the worm II terminates at the top of the worm in a continuous groove III). A follower lever I8 is pivoted at one end on a pin I9 which is secured to the casing I2a and engages an elongated slot I8a in the lever. A tooth I8?) is provided on the other end of the lever for engagement with the thread of the Worm II. A biasing spring 20 is provided to normally hold the lever I8 away from the worm as shown in the drawing, and a magnet 2I, energized in parallel with the fuel-feeding motor, is arranged to attract armature I80 mounted on: lever I8 and to shift the lever I8 so that the tooth I8b engages the thread on the worm II. A link 22 is provided on the lever I8 for the purpose of operating any of the various air controlling devices shown in the drawing, such as operating the dampers 6b, 6c in Figures-1 and 2 or for controlling the circuit of the damper mag net in Figure 3, or for controlling the circuit of motor la in Figure 4. As shown in Figure 1, magnet 2| is connected in parallel with motor I by leads 2Ia.

It will be understood that as soon as the fuelfeeding motor is energized, magnet 2I causes engagement of the lever I8 with the worm I'I. Rotation of the worm slowly raises the left end of lever I8 until it reachesthe continuous groove IIb where it remains as long as the fuel-feeding motor is in operation." As lever I8 is raised by the worm, link 22 connected to the air controlling device opens damper 6b and increases the amount of air supplied to the burner. As soon as the fuel-feeding motor is de-energized, magnet 2I releases the armature I80 and lever I8 is retracted from engagement with worm II by spring 2|], and the lever I8 then returns to. its lower or starting position.

An adjustable stop 22a is secured to lirik22 and serves to limit the downward movement of the link. By varying the position of stop Me on link 22, the time of operation of the time delay device may be set'at any desired value within certain limits.

In the operation of the arrangement shown in Figure 1, the mechanism II will energize the motor I at periodic intervals of short duration, 50 long as the space to be heated does not require any additional heat. This intermittent operation of the Stoker is for the purpose of preventing the fire from dying out. a As soon as the temperature of the space being heated falls below a' definite limit, the thermostat I completes a circuit and causes operation of the stoker until the temperature in the space to be heated is brought back to normal. During the shut-down periods, the coal burns around the edge of the .tuyere and leaves a ring of ash around the outer edge of the tuyere as indicated by. the dotted area 4a in Figure 1, the hot spot of the fire 4b beinglocated at the center of the tuyere. .In the systems now commonly in use, the full blast of air is supplied to the air chamber 5 surrounding the tuyre 4 as soon as the motor I begins operation, and the ring of ash 4a is violently blown upwardly into the combustion chamber lb, into the flue Ito and out the chimney 3. Some of the flyash filters through small cracks or openings around the doors of the furnace, :or in the various joints, and is carried into other'parts of the room. According to my invention, however,-the damper 6b is normally set in a position such that the amount of air supplied to the air chamber 5 is insufiicient to cause any substantial blowing of the fly-ash from around the rim of the burner. Accordingly, by arranging for sufficient time delay in the operation of the damper-operating device after motor I begins to operate, the fuelfeeding mechanism will supply enough coal to the tuyre to displace the ash from directly over the air openings in the tuyre by the time the damper 6b is fully open and the full blast becomes effective. As soon as the air openings in the tuyre become covered with unburned coal, the force of the air stream is thereby cut down and there is no substantial blowing of the flyash.

. The amount of air supplied to the burner may be controlled by a damper 60 located in the supply duct 6 a as illustrated in Figure 2. It will be understood that the damper 6c is normally adjusted to supply a small amount of air to the burner,

but insufficient to cause any substantial blowing of the fiy-ash. The time-delay device I2 may be according to any of the constructions shown in Figures 1a, 1b and 1c. The dotted line He represents the driving connection between shaft Na and the shaft of fuel-supply motor I.

Instead of having the time-delay device control the damper directly, the dampermay be operated. by an electromagnet- I3 as shown in Figure 3, and the circuit of the electromagnet is controlledby a switch 221) operated by the link 22 of the time-delay device I2 which-may assume the form of any of the devicesshown in Figures 1a, 1b, and'lc. I

In Figure 4, I have shown a modified control arrangement in which-the motor I is employed for driving the fuel-feeding arrangement, and a separate motor I a is provided for driving: the blower. The motor I is controlled by the intermittent control device I I in the same manner as in the other arrangements, and the motor la is energized by a circuit connected in parallel with the terminals of motor "Ithrough a switch 22b operated by time-delay'device I2 which may assume any of the formsfshown in Figures 1a, :1b, and1c. In this arrangement, the motor I beginsto operate and to supply fuel to the tuyere 4, :and a; predetermined timeelapses before the switch 22b. closes the'c ircuit' to the blower motor-1a.; Accordinglmby adjusting the time delay of the devicel 2, themotor I will feed enough coal to'the tu'yere to displace the ash fromabove the air opening in the tuyere, 1 I

In Figure 1121 have illustrated a modified construction of time-delay device in which elements serving similar functions to corresponding 'elements in Figure la are indicated by like-reference numerals. In this arrangement, the worm I! is mounted upon the shaft I IIa which in turn is driven from the motor I, the same as in Figure la. Instead of employing a pivoted lever for operating the link 22 by engagement with the worm II, the link'22 in Figure. lb is secured to a sliding carriage 23 which is mounted for vertical sliding movement upon shaft H11 and upon rod 23a mounted parallel with the shaft "Ila. Magnet 2| is mounted upon carriage 23 and a bell-crank armature 23b is provided for the magnet 2|. A finger 23c, carriedby' the fre'e 'end of the bell-crank lever is arrangedto engage the thread on the worm II when magnet .2! is energized'. The spring 20 normally 'b'iases' armature 23b in a direction to disengage finger 23c-Lfrom the worm. II. Adjustable stop 22a, mounted upon link 22, engages the-lower wall of casing I2a and serves to limit the downward movement of carriage 23, and, as in the case of Figure-1a,

adjustment of the position of this stop. effects adjustment inthe time of operation of the time- 'delay .device.- The operation of Figure '1b is believed to be clear from the foregoing description of operation of Figure 1a. 1

In Figure 10, I have illustrated a further modification of the time-control device which employ a centrifugal governor 24, driven from the shaft Ila for shiftingthe lever I8 into engagement with the worm H, as soon as the motor Treaches a predetermined speed. The gov- :ernor 24 maybe of any suitable construction,

and simply for the purpose of illustration, I have shown the governor as comprising the well known construction of pivoted arms, having weights attached thereto, mounted upon a shaft 24a which is driven from shaft Ha -by means of worm gear Ill) and worm l'lc. Lever I8 is pivoted at one end to a point intermediate the ends of a second lever I802, which in turn is pivoted at one end [8e to the supporting frame l2a. The opposite end of the lever l8d is provided with a fork which engages in the groove of movable collar 24b of the governor 24. Spring 20 normally biases lever "id in a direction to disengage lever |8 from worm I! when the shaft Ila is stationary or turning at a speed below a predetermined speed.

In the, operation of the arrangement shown in Figure 1c, the shaft Na, and, therefore, the governor 24, is driven at a speed proportional to the speed of the fuel-feeding motor 1. When the motor is first energized, the parts of the time-delay device are in the position shown in Figure 1c. The motor comes up to full speed rather quickly and the governor 24 moves the lever l8 into engagement with worm I! and thereafter lever 18 travels upwardly in contact with worm 11 until it reaches the continuous groove [1b where it remains as long as motor 1 continues in operation. As soon as the motor 1 stops operating, governor 24 ceases to exert any pull on :lever [8d and spring 20 withdraws the lever l8 from engagement with worm l1 and the parts are returned to the starting position shown in Figure 10.

From the foregoing, it will be seen that in all forms of my time-delay device, the {movable element 22 is mechanically driven by the fuelfeeding motor from a starting position to an operating position by means of the worm I1. Furthermore, in all three modifications, the driving connection between the motor I and the movable element 22 embodies a releasable clutch device which is normally open when the motor 1 is de-energized. The clutch device in each case is controlled according to an operating condition of the fuel-feeding motor. In Figures 1a and 1b the clutch device is controlled by magnet 2| in accordance with the voltage applied to the motor, while in Figure 1c the clutch device is controlled by governor 24 in accordance with the speed of the motor. In all three forms of the device the movable member 22 is normally biased by gravity to the lower or starting position, but springs may be used to supply the biasing force if desired. Motor 1 is preferably a constant speed motor, although no'special type of motor is required.

. My invention not only reduces and/or substantially prevents the blowing of fly-ash, but it also improves the efficiency of operation of the burner. This latter advantage is realized by reason of the fact that the full blast of air is not applied at the beginning of each period of operation,

but is delayed until unburned coal covers all of the air openings in the tuyre. In this manner, the air blast is rendered completely effective for promoting combustion of the coal and none of the. air is lost by passing through. openings in the'tuyre which is uncovered by reason of the am having beenblown away. Since there is'no substantial amount of air wasted by passing through uncovered tuyre openings, the opera-' tion of the burner is more efficient, the temperature of the furnace rises quicker, and each airto said burner normally arranged to restrict the flow of air to less than full blast, a worm driven by said fuel supply means, a follower operated by said worm, a connection from said follower to said damper for operating said damper, means for normally biasing said follower out of engagement with said worm, and means rendered operative u-pon starting said fuel supply means for moving said follower into engagement with said worm.

2. In combination, a solid fuel burner, means including a motor for supplying fuel to said burner, a blower for supplying air to said burner, a damper for controlling the flow of air to said burner normally arranged to restrict the flow of air to less than full blast, a movable element for opening said damper, driving means for mechanically operating said movable element from said fuel supply motor and including a normally open clutch element, and means responsive to an operating condition of said fuel supply motor for operating said clutch element.

3. A combination according to claim 2 wherein said clutch operating means comprises an electromagnet energized in parallel circuit relation with the fuel supply motor.

4. A combination according to claim 2 wherein said clutch operating means comprises a centrifugal governor driven by the fuel supply motor and adapted to operate said clutch when said motor reaches a predetermined speed.

5. In combination, a solid fuel burner, intermittently operating means including a motor for supplying fuel to said burner, a blower for supplying air to said burner, a damper for controlling the flow of air to said burnernormally arranged to restrict the flow of air to less than full blast, a worm driven by said fuel supply motor, a follower operated by said Worm, means for normally biasing said follower out of engagement with said worm,means rendered operative upon starting said fuel supply means for moving said follower into engagement with said worm, and means controlled by said follower for operating said damper to full draft position a predetermined time after the starting of said motor.

6. A combination according to claim 9 wherein said fuel supply means is driven by one motor and said air-supply means is driven by a separate motor, and including a normally open switch in the circuit of said air-supply motor, said switch being operated by said follower to close the circuit of said air-supply motor a predetermined time after starting of said fuel supply motor.

7. In combination, a solid fuel burner, intermittently operating means for supplying fuel to said burner, means for supplying air to said burner, said air supplying means being normally ineffective to supply full blast of air, a worm driven by said fuel supply means; a follower operated by said worm, a connection from said follower to said air supplying means for controlling said air supplying means, means for normally biasing said follower out of engagement with said worm, and means rendered operative upon starting said fuel supply means for moving said .clutch element, and means responsive to an operating condition of said fuel supply motor for operating said clutch element.

' 9. In combination, a solid fuel burner, intermittently'operating means including a motor for supplying fuel to said burner, means for supplying. air to said burner, said air supplying means being normally ineffective to supply full blast of air, a, Worm driven by said fuel supply motor, a follower operated by said worm, means for normally biasing said follower out of engagement with said worm, means rendered operative upon starting said fuel supply means for moving said follower into engagement with said worm, and means controlled by said follower for rendering said air supplying means operative to supply full blast of air to said burner a predetermined time after the starting of said motor.

10. A combination according to claim 9 wherein said means for moving said follower into engagement with said worm comprises an electro magnet energized simultaneously with said fuel supply motor.

11. A combination according to claim 9 wherein said means for moving said follower into engagement with said worm comprises a centrifugal device driven by said fuel supply motor.

ERNEST T. SELIG, JR. 

